托福听力TPO17原文Lecture4

托福听力TPO17原文Lecture4

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TPO17Lecture4Biology

Professor：Ok,now I want to talk about an animal that has a fascinating set of defense mechanisms. And that’s the octopus,one of the unusual creatures that live in the sea.The octopus is prey to many species,including humans,so how does it escape its predators?Well,let me back up here a second. Anyone ever heard of Proteous?Proteus was a God in Greek mythology who could change form.He could make himself look like a lion or a stone or a tree,anything you wanted,and he could go through a whole series of changes very quickly.Well,the octopus is the real world version of Proteus.Just like Proteus,the octopus can go through all kinds of incredible transformations.And it does this in three ways:by changing color,by changing its texture,and by changing its size and shape.For me,the most fascinating transformation is when it changes its color.It’s a normal skin color,the one it generally presents,is either red or brown or even grey,and it’s speckled with dark spots.But when it wants to blend in with its environment to hide from its enemies,it can take on the color of its immediate surroundings:the ocean floor,a rock,a piece of coral,whatever.Charles?

Student：Do we know how that works,I mean,how they change colors?

Professor：Well,we know that the reaction that takes place is not chemical in nature.The color changes are executed by two different kinds of cells in the octopus’skin,mainly by color cells on the skin’s surface call chromatophoresChromatophores consist of tiny sacks filled with color dye.There might be a couple hundred of these color sacks per square millimeter of the octopus’skin,and depending on the species,they can come in as many as five different colors.Each one of these sacks is controlled by muscles. If the muscles are relaxed,the sack shrinks,and all you see is a little white point.But if the muscle’s contract,then the sack expands,and you can see the colors.And by expanding different combinations Student：And just with various combinations of those five colors,they can recreate any color in their environment?

Professor：Well,they can no doubt create a lot with just those five colors,but you are right,maybe they can’t mimic every color around them,so that’s where the second kind of cell comes in.Just below the chromatophores is a layer of cells that reflect light from the environment,and these cells help the octopus create a precise match with the colors surround them.The colors from the color sacks are supplemented with colors that are reflected from the environment,and that’s how they are able to mimic colors with such precision.So,that’s how octopus mimic colors.But they don’t just mimic the colors in their environment; they can alos mimic the texture of objects in their environment.They have these little projections on their skin that allow them to resemble various textures.The projections are called papillae6If the octopus wants to have a rough texture,it raises the papillae.If it wants to have a smooth texture,it flattens out the papillae, so it can acquire a smooth texture to blend in with the sandy bottom of the sea.So the octopus has the ability to mimic both the color and the texture of its environment.And it’s truly amazing how well it can blend in with its surroundings.You can easily swim within a few feet of an octopus and never see it.

Student：I read that they often hide from predators by squirting out a cloud of ink,or something like that.

Professor：Yes.The octopus can release a cloud of ink if it feels threatened.But it doesn’t hide behind it,as is generally believed.Um,the ink cloud is...it serves to distract a predator while the octopus makes

its escape.Um,now there’s a third way that octopus can transform themselves to blend in withor mimic their environment,and that’s by changing their shape and size,well,at least their apparent size.The muscular system of the octopus enables it to be very flexible to assume all sorts of shapes and postures.So it can contract into the shape of a little round stone,and sit perfectly still on the seafloor.Or it can nestle

up7in the middle of a plant and take the shape of one of the leaves.Even Proteus would be impressed,I think.

教授：好的，现在我想讲一讲一种特别的动物，它有一套令人惊叹的防御机制——它就是章鱼，一种生活在大海之中的不凡之物。章鱼的天敌包括人类在内的很多物种的捕食者，那么，它是怎样逃脱它的捕食者的呢?好的，我先讲些背景知识吧!有谁知道普罗透斯吗?普罗透斯来自古希腊神话中的一位海神。他可以变形，使自己看上去像一头狮子或者石头、树木，你们能想到的一切，并且他能够在很短的时间之内完成变形。嗯，章鱼是真正存在的现世版的普罗透斯。和他一样，章鱼也能完成各种不可思议的变形。同时，它可以用三种方式变形：改变颜色、改变纹理、改变大小和形状。对我而言，最有趣的当属改变颜色这项了。它没有变色时的一般肤色，既可能是红的，棕色的，甚至灰色的，体表点缀有许多黑色的斑点。但是，当它试图和环境混同为一个颜色以趋避天敌时它马上就能变成周围景物的颜色：大海的、岩石的、珊瑚，什么都行。查尔斯，你有什么问题?